White Spots on a Zinnia

Fungus

• When zinnia leaves and stems look as if they have white blotches of powder on them, the powdery mildew fungus is probably the culprit. Powdery mildew occurs most often when weather is humid and hot. As the fungus spreads and progresses, leaves wilt and fall from the plant. Rust is another type of fungus, which contradicts its name by creating whitish, powdery spots on flowers, buds, leaves and stems instead of reddish discoloration. Rust may spread to cover entire leaves and blossoms.

Blight

• Botrytis blight creates tan and brown spots on leaves that become covered with fuzzy, whitish or grayish lesions. Botrytis blight occurs most often during wet, humid weather. Blight, also known as alternaria leaf spot, creates spots on plants with grayish or whitish centers surrounded by red-brown rings. The centers of the spots drop out, leaving holes in leaves.

Rot

• Root rot is a fungal disease that creates white, cotton-like lesions around the base of zinnias. Leaves may become yellowed or wilted as the fungus progresses. Stem rot creates discoloration around the stem and causes wilting of the entire zinnia plant. Like root rot, stem rot creates cotton-like patches of growth around the base of zinnia plants. Crown rot makes leaves wilt and drop from the plant. Around the bottom of the plant, spreading white fungal growth occurs when crown rot is present.

Control

• Do not overcrowd zinnia; space them out during planting to allow for adequate air flow between each plant. As soon as you notice symptoms of fungal disease on plants, remove all infected plant parts and discard. When watering plants, point the moisture near the base of zinnias. Water on leaves and flowers will only encourage fungal growth.